Recently, with the spread of personal digital assistants (PDA), palm top computers, portable game equipment, etc., a touch panel formed on a transparent substrate has been used widely as an input means that can be combined with a display device.
For example, in a liquid crystal display device as a touch-panel-equipped display device, a transparent touch panel is laminated on an image display surface of liquid crystal panel, and an image displayed on the liquid crystal panel can be viewed through the touch panel. Such a liquid crystal display device is configured so that when a surface of the touch panel on a viewed side, that is, a surface thereof on which display images on the liquid crystal panel are observed, is pressed with a fingertip or an input pen in response to an image displayed thereon, the pressed position can be detected. This allows input contents to the touch panel to be reflected on the control of used equipment such as a PDA.
An electrostatic capacitance touch panel as an exemplary touch panel in which a transparent substrate is used has the following configuration: touch electrodes formed of transparent conductive films are formed as two-dimensional patterns on an insulative transparent substrate such as a glass plate or a film. Particularly, a projection-type electrostatic capacitance touch panel having touch electrodes arranged at predetermined intervals is capable of detecting a plurality of touched points at the same time, that is, applicable to so-called multitouching. Therefore, it particularly has attracted attention in recent years.
In such an electrostatic capacitance touch panel, touch electrodes formed in an area that overlaps an image display surface of a display panel are formed with transparent conductive films. On the other hand, connection terminals for outputting potentials of touch electrodes to an external circuit board, and lead lines for connecting the touch electrodes and the connection terminals are formed with metal layers made of a metal material such as aluminum, which has a lower resistance than that of the transparent conductive film. In the case where metal layers are used as connection terminals or lead lines, surfaces of the metal layers are covered with protective films so that oxidation or exfoliation of the metal layers is prevented. However, at least a part of each connection terminal should not be covered with a protective film, but has to be exposed, because they are connected to connection members such as a flexible printed circuit board (FPC) that connects the touch panel and external circuits.
FIG. 33 are cross-sectional views showing exemplary steps of a conventional process for manufacturing an electrostatic capacitance touch panel. It should be noted that in each of FIG. 33(a), FIG. 33(b), and FIG. 33(c), the left-side illustration shows a cross section of a part where a touch electrode is formed, that is, a cross section of a part A taken along an arrow line A-A′ in FIG. 1 showing electrode patterns. Further, in each of FIG. 33(a), FIG. 33(b), and FIG. 33(c), the central illustration shows a cross section of a part where a lead line is formed, that is, a cross section of a part B taken along an arrow line B-B′ in FIG. 1 showing the electrode patterns. Still further, in each of FIG. 33(a), FIG. 33(b), and FIG. 33(c), the right-side illustration shows a cross section of a part where a connection terminal is formed, that is, a cross section of a part C taken along an arrow line C-C′ in FIG. 1 showing the electrode patterns.
As shown in FIG. 33, in the conventional touch panel manufacturing method, an aluminum (Al) layer and a molybdenum (Mo) layer covering the aluminum layer are formed by sputtering sequentially over an entire surface of a transparent substrate 701 formed of glass or a transparent film, and a resist film is formed thereover. Then, this resist film is exposed and developed by using a mask in such a manner that the resist film remains only on portions where lead lines and connection terminals are to be formed. Thereafter, etching is carried out using the remaining resist film as a mask. As a result, as shown in FIG. 33(a), metal layers each of which is made of a laminate of an aluminum layer 711 and a molybdenum layer 712 are formed on portions where lead lines and connection electrodes are to be formed.
Subsequently, on the transparent substrate 701, a transparent conductive film layer such as ITO (indium tin oxide) is formed by sputtering. Then, after a resist film (not shown) is applied on the transparent conductive film layer, the resist film is exposed and developed so as to remain on the touch electrode portions and the connection terminal portions. By etching the transparent conductive film layer by using this resist film as a mask, transparent conductive film layers 713 are formed on the laminates each of which is composed of the aluminum layer 711 and the molybdenum layer 712, on the touch electrode portions and the connection terminal portions. The configuration in which the transparent conductive films 713 are formed is shown in FIG. 33(b).
Thereafter, a protective film 714 made of SiN, SiO2, or a transparent resin are formed over an entirety of the transparent substrate 701 by CVD or the like. Then, the protective film 714 is etched by using a resist pattern, whereby openings 715 are formed at the connection terminal portions.
Thus, the touch panel provided with touch electrodes 702, floating electrodes 703, lead electrodes 704, and connection terminals 705 as shown in FIG. 33(c) is produced. Here, the touch electrodes 702 are formed with transparent conductive film layers 713 formed as two-dimensional patterns. The floating electrodes 703 are formed with the transparent conductive film layers 713 provided between the touch electrodes 702. Each of the lead electrodes 704 is formed of the laminate of the aluminum layer 711 and the molybdenum layer 712. Each of the connection terminals 705 is formed of a laminate of the aluminum layer 711, the molybdenum layer 712, and the transparent conductive film layer 713. It should be noted that in this touch panel, the protective film 714 made of a transparent resin is formed over an entire surface of the panel except for the openings 715 above the connection terminals 705.
The following description explains another exemplary conventional method for manufacturing a touch panel. In the case where the touch electrodes are finely patterned, or in the case where lead lines are provided in narrow areas, lead lines are formed in a two-layer structure on a transparent substrate so that those in one layer should not be conductive with those in the other layer. In this case, connection terminals are also formed in a two-layer structure so as to match the layers where the lead lines connected with the connection terminals are formed.
FIGS. 34 and 35 are cross-sectional views showing exemplary steps of a process for manufacturing an electrostatic capacitance touch panel in which lead lines are formed in a three-dimensionally two-layer structure.
It should be noted that in each of FIGS. 34(a) to 34(c), and FIGS. 35(a) to 35(c), the left-side illustration shows a cross section of a part where a touch electrode is formed, that is, a cross section of a part D taken along an arrow line D-D′ in FIG. 6 showing electrode patterns of a touch panel having lead lines divided in two layers. Further, in each of FIGS. 34(a) to 34(c) and FIGS. 35(a) to 35(c), the central illustration shows a cross section of a part where the lead lines are formed, that is, a cross section of a part E taken along an arrow line E-E′ in FIG. 6 showing the electrode patterns. Still further, in each of FIGS. 34(a) to 34(c) and FIGS. 35(a) to 35(c), the right-side illustration shows a cross section of a part where connection terminals are formed, that is, a cross section of a part F taken along an arrow line F-F′ in FIG. 6 showing the electrode patterns.
First, an aluminum layer and a molybdenum layer covering the aluminum layer are formed sequentially by sputtering over an entire surface of a transparent substrate 801 made of glass or a transparent film, and a resist film is formed thereover. Then, this resist film is exposed and developed in such a manner that the resist film remains only on portions where lead lines and connection terminals are to be formed in a first layer, that is, a lower layer that is formed immediately on the transparent substrate. Etching is carried out using this remaining resist film as a mask. As a result, as shown in FIG. 34(a), laminates each of which is made of an aluminum layer 811 and a molybdenum layer 812 are formed on portions where lead lines of the first layer and connection electrodes of the first layer are to be formed.
Subsequently, as shown in FIG. 34(b), a protective film 813 of the first layer, which is made of SiN, SiO2, or a transparent resin and has a function as an interlayer insulative film between the first layer and a second layer, is formed by CVD or the like.
Next, an aluminum layer and a molybdenum layer covering the aluminum layer are formed sequentially by sputtering over the protective film 813 thus formed for the first layer, and a resist film is formed thereover. Then, this resist film is exposed and developed in such a manner that the resist film remains only on portions where lead lines and connection terminals are to be formed in the second layer, that is, an upper layer on a surface side of the touch panel. Thereafter, etching is carried out using this remaining resist film as a mask. As a result, as shown in FIG. 34(c), laminates each of which is made of an aluminum layer 814 and a molybdenum layer 815 are formed on portions where lead lines of the second layer and connection electrodes of the second layer are to be formed.
Next, the patterned resist film is caused to remain on the protective film 813 of the first layer, except for areas above the laminates of the aluminum layer 811 and the molybdenum layer 812 that are to become the connection terminals of the first layer. The protective film 813 of the first layer is etched by using this resist film as a mask, whereby an opening 816 is formed and a surface of the molybdenum layer 812 is exposed. This state is shown in FIG. 35(a).
Subsequently, a transparent conductive film layer made of ITO or the like is formed by CVD or the like on a surface of the protective film 813 of the first layer. Then, a resist film is formed so as to be patterned in accordance with two-dimensional patterns of touch electrodes and floating electrodes formed between the touch electrodes. Here, at the same time, the resist film is caused to remain in the part F where the connection terminal is to be formed, in such a manner that the resist film covers the opening 816 of the protective film 813 of the first layer. Then, etching is carried out by using this resist film, so that the transparent conductive film layer 817 thus patterned remains on portions in the part D where the touch electrode and the floating electrode are to be formed, and on a portion in the part F to cover the connection terminal of the first layer, as shown in FIG. 35(b).
Next, over an entire surface of the transparent substrate 801, a protective film 818 of the second layer, made of SiN, SiO2, or a transparent resin is formed by CVD. A resist film is formed in a patterned form such that the resist film remains on the protective film 818 of the second layer except for areas where the connection terminal of the first layer and the connection terminal of the second layer are to be formed. Etching is carried out by using this resist film as a mask, so that openings 819 and 820 are formed in the protective film 818 of the second layer. As a result, as shown in FIG. 35(c), a touch panel is produced that is provided with the floating electrode 803, the lead electrode 804a of the first layer, the lead electrode 804b of the second layer, the connection terminal 805a of the first layer, and the connection terminal 805b of the second layer. Here, the floating electrode 803 is covered with the protective film 818 of the second layer, and is formed between the touch electrodes 802. Surfaces of the connection terminal 805a of the first layer and the connection terminal 805b of the second layer are exposed in openings 816, 819, and 820 provided in the protective film 813 of the first layer and the protective film 818 of the second layer.
It should be noted that, for example, JP2008-233976A proposes that in the case where the lead lines and the connection terminals, together with touch electrodes, are formed with transparent conductive layers, portions of the transparent conductive films where the touch electrodes and the lead lines are connected are made thicker than the touch electrode portions, so that the electric conduction between the touch electrodes and the lead lines is ensured further.